1. Technical Field
Embodiments of the present invention generally relate to a developing device; and a process unit and an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction machine including at least two of these functions, that include a developing device.
2. Description of the Related Art
In general, electrophotographic image forming apparatuses such as copiers, printers, facsimile machines, or multifunction machines including at least two of these functions include a developing device to develop latent images formed on an image bearer with developer, and a toner container (i.e., a toner cartridge) for containing developer such as toner. As the toner in the development device is consumed in image development, fresh toner is supplied from the toner container to the developing device. If mixing of the toner supplied from the toner container and the toner existing in the developing device is insufficient, the ratio of supplied toner becomes uneven between a portion adjacent to a toner supply inlet formed in the developing device and other portions inside the developing device. In such a state, it is possible that image density becomes uneven or toner scatters on the backgrounds of output images.
Therefore, toner is circulated inside the developing device to equalize the state of toner (the ratio of the supplied toner) inside the developing device. For example, an interior of the development housing (or a casing) is divided with a partition into first and second compartments that communicate with each other in both axial end portions, and conveyance members such as conveyance screws are provided in the first compartment and the second compartment, respectively, to transport the toner therein. Toner is supplied from the toner cartridge to the first compartment, and a developing roller is provided in the second compartment. The conveyance screws transport the toner in the respective compartments in the opposite directions, and the toner transported to an end portion in one compartment is transported through a communication opening at the end of the partition to the other compartment. Then, toner is transported by the conveyance screw to the opposite end portion, after which the toner moves through the communication opening again to the other compartment. Toner can be circulated between the first compartment and the second compartment by repeating this operation. Accordingly, the supplied toner can be mixed with the toner existing in the developing device, and the ratio of supplied toner can become uniform.
Even in developing devices in which developer is thus circulated, it is possible that the amount of toner therein decreases to a degree that image density becomes insufficient if toner is not timely supplied to the developing device.
For example, JP-2012-155141-A proposes, for controlling the timing of toner supply, providing an optical sensor, as a developer amount detector, to the first compartment to which toner is supplied and detecting the amount of toner remaining therein according to changes in the amount of light in a detection area thereof.